[Pw_forum] correct volume for effective charge calculation for supercell

Paolo Giannozzi giannozz at democritos.it
Sat Feb 11 12:27:16 CET 2012

On Feb 11, 2012, at 8:08 , KORIR KIPRONOH wrote:

> I'm still seeking more clarification on the same subject, born  
> effective
> charge is a product of "cell volume" with derivative of the  
> polarization
> with respect to atomic displacement at zero macroscopic  
> field........so
> I thought there is dependence on volume?

I am not sure I understand what you mean. If you have a finite object
(or simply, a molecule) in a supercell, yes, the effective charges
decrease as the volume of the supercell increases. This is normal:
the dipole does not depend upon the volume of the supercell
(if it is large enough), the dipole per unit volume does.

Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222

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